A chance to blame extreme weather on climate change

When extreme weather strikes, somebody, somewhere always asks about a link to climate change. It's time we gave straight answers

By Peter A. Stott

IN THE aftermath of hurricane Katrina in 2005, a vigorous debate raged as to whether it was a “normal” natural disaster or a consequence of global warming. Al Gore depicted the devastation of New Orleans in his movie An Inconvenient Truth and linked it to climate change. I became involved during a case before the High Court in London challenging a UK government decision to distribute the movie to schools. I was asked to provide expert written evidence on the extent to which the film correctly represented scientific understanding at the time.

I liked the film and thought that Gore’s presentation of the causes and likely effects of climate change was broadly accurate. As the Intergovernmental Panel on Climate Change (IPCC) concluded in its most recent assessment report&colon; “warming of the climate system is unequivocal, as is now evident from observations of increases in global average air and ocean temperatures, widespread melting of snow and ice, and rising global average sea level”. And as data continues to pile up, the evidence gets ever stronger that human-induced emissions of greenhouse gases are the main cause of the observed warming over the past century.

But hurricanes are difficult. Climate models predict that they will become more intense. At the same time, considerable uncertainty remains. We only have about 40 years of reliable observational records, which precludes a clear determination of their variability. Given that different aspects of climate change could act to increase or decrease hurricane activity, whether or not Katrina can be ascribed to global warming is a challenge beset by difficulty.

It is not surprising, then, that in the aftermath

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